How to successfully transfer one .blend to another computer and keep everything intact?
Video files and image sequences are not packed as part of the blend file.
Why? because they would create an impractically large file.
No video editing program stores the media and the projects on a single file.
The way you transfer the project is you bring along all of the files that are linked to the project. If you want a single file to transport/upload, then zip the folder with all the elements and the project.
But it is more practical to put your files in an external drive and plug it in to to the new computer and re-link.